1. Field of the Invention
An embodiment of the present invention relates to a method of forming a metal oxide thin film including deposition of one monolayer by alternately feeding a source gas and an oxidizer gas to a substrate.
2. Description of the Related Art
In contrast to the CVD which is a method adapted to deposit a film continuously by incessant feed of materials, the atomic layer deposition method (hereinafter will be referred to as “ALD method”) is a method of depositing individual films each comprising a single layer of a substance step by step and is excellent in deposition of a strictly controlled layer of high quality.
Known metal oxide film deposition methods utilizing the ALD method include: (1) a method of forming a metal oxide thin film by alternately feeding a source gas comprising a hydrolyzable metallic compound and an oxidizer gas (comprising H2O or O2 for example); (2) a method using a metal chloride and a metal salt as a source gas and an oxidizer gas, respectively, to form a metal oxide film, specifically, using Hf(NO3)4 (hafnium nitrate) and HfCl4 to form an HfO2 film or using Hf(NO3)4 and AlCl3 or ZrCl4 to form an HfAlOx or HfZrOx film, as described in Appl. Phy. Lett. 84. P398 (2004); and (3) a method using such a chloride as AlCl3, HfCl4 or SiCl4 and a metal alkoxide to form a compound metal oxide thin film (comprising TiAlOx, ZrAlOx, HfAlOx, ZrTiOx, HfTiOx, or ZrSiOx), as described in SCIENCE Vo.288 P319 (2000).
In depositing a compound metal oxide (comprising two or more kinds of metal oxide) by the conventional ALD method, the aforementioned method (1) needs to repeat six steps consisting of feed of metal gas A→gas purge→feed of oxidizer gas→gas purge→feed of metal gas B→gas purge→feed of oxidizer gas→gas purge. Thus, multiple gas feed steps are required, which results in a problem that the film deposition time taken by the ALD method, which essentially involves a film deposition speed problem, is further prolonged.
The aforementioned method (2) is capable of forming a compound metal oxide film (comprising HfZrOx for example) by repeating four steps consisting of feed of source gas (comprising a metal chloride, for example, ZrCl4)→gas purge→feed of oxidizer gas (comprising a metal salt, for example, Hf(NO3)4)→gas purge. However, the method (2) can form only limited kinds of compound oxide because of the use of metal salt.
The aforementioned method (3) using a metal alkoxide involves a similar drawback that only limited kinds of metal alkoxide can be used as oxidizers and, hence, only limited kinds of compound metal oxide can be deposited as film because metal alkoxides inherently have high hydrolyzability.
Accordingly, it is an embodiment of the present invention to provide a method which can solve the foregoing problems at a time and which is capable of forming metal oxide thin films of diverse kinds including, in particular, a compound metal oxide thin film comprising different kinds of metal by utilizing the ALD method without affecting the film deposition speed.